Compensating test-plate for illumination measurements.



.C. H. SHARP.

COMRENSATING TEST PLATE FOR ILLUMINATION MEASUREMENTS. APPLICATION FILED APR.9, I915.

1,185,012. Patented May 30,1916.

T .I A

z I //r//.// //////A- 0 FFII IjIII I I T I l I g G) z n tor Atlorncya.

omitmag/ concern; I v 1* B t known'lthat LQCLAYTON H. SHARr,a

of; the United States, resident of lains, Westchester. county, State of ork,.1 \have invented" a certain new and f Compensating Test-Plate. for 11111 1111 nts, .o'f which the followb10111: Measureine gtisajspec'ficationi:

q This glIW' tion relates to Improvements in were a ed n rt a w values are measured by ob photometric apparatus, the plane' difiusing plate receivatusis calibrated byproduciingaon the 1 known illumination A' plate. S ill not; however, givecorrect values; lumination; ,under all circumstances unacts} asiia" perfect difiu'ser of light it and hejibrightnessiproducedl is" proportional fi'theanglewof incidenceof the ects ,of invention are to proest-i late which will obey the cosine of Lambert and which will permit the on y te measurement of illumination irre-' tiveioff flthe angle of, incidence of the g t; These further objects will more appear fromf fthe following specifican nd. accompanying drawings, consid- Id together or sepa-rately. 1 a

Inithe;drawings} Figure, 1 is an elevation, rtly .11 in section, of a .test plate and a phometer, saidagitest-plate embodying my im oved inventionyFigi 2 is a plan view of h same, Fig. 3 is a plan view, on an en ged; SCale jOf. OIIG llalf of the test-plate bodying my inventionyFigi l is a section hroughatheggreatest diameterof the same; g. .15 q is au'bottom View of the same; Fig. 6 1 sectional view ofz'a modifica'tion Fig;

and Fig-8iis a'sectional View of anodificationg; 1 M1 i I In ll views like parts are designated by amereferencecharacters. ejferring to v Figs. 1 and ;2,. the test-plate ssociated withaa photometer 2. The larx photometer illustrated forms no rt f theipresentiinvention, but 1s shown meansawherein my improved test-plate ary to that disclosed in the. patent to 'illumlnation "to be? measured. The

the cosineilawiofLambert which states sectional view of another modificausedut The photometerillustrated is AT T QF C MIiIlL T SAITNGLTES'LQPLATE FOR InIJIiMI NnTIon lvrnasuizn unnrs.

' ratent ama sdiaie.

. r The photometer Sharp and Millar,No. 960420, dated June illustrated has sight tube 3, through which the illumination is viewed from a prism 4.- The prism permits the vlewing of the illumination on a comparison plate 5, which is illuminated by means of ancomp'arison lamp 6. The distance ofthis lam'pfrom the plate is'controlled by "means-of an actuating knob and a cord runnlng over pulleys, asshown. The dis- I tance between the lamp and the plate'b is measured upon a scale 8.; On the side of the sighttube opposite the plate 5 is a mirror-9 supported in an elbow tube 10. a At the open end of the tube 10is thetest-plate A (Fig. 1). The test-platewill be: illuminated by the light to be measured andi'theobserver can adjust the position of the comparison lamp in relation to the comparison plate so that the two plates, A and 5, will show the same brightness. The distance of the lamp from the comparison plate-willthenbe indicated upon the scale, and the foot candle illuminationindicated.

The plate A includes aplane member 1 preferably of translucent white glass roughened onnboth surfaces. The member 1 is associated with the translucent dilfusingf ring 11. This ring "is preferably made of translucent white glass also preferably roughened on both surfaces.

12 is a sleeve of opaque material.

13 is a shield of a definiteheight'carried' 'by a suitable opaquesupporting plate 14.

required amount when the angle of incidence is large, due. to the excessive lossof light by reflection atthese angles. If light be admitted throughthe ring 11 to the am derside ofthe memberl in sufficient amount it will compensate for the deficiency in transmitted light through the member 1. It will be observed that at normal incidence, i. 6. 90 to the plane ofthe member 1 (see the vertical broken lines in Fig. 4) no light will strike the sides offthe diffusingring 1-1', hefnc'ef a ll iof the; light, will i'lluminate the member "1'.- Asthe angle of incidence of the V I :light on the member 1jincreases, more light qwill pass' through -lthe diffusing ring 11.- This increase offthe ,light-incident ijon the sides of. the 'difiusingring 11 inoreaseswithf I the "sine ofgthetiangle of incidence on 1the. "'meinberfl, and by properly proportioiiin'g" thepartsw the'increa'se of brightness on the" underside of the member, 1 may be made such as .to compensate at all angles ;-for the; Tdeficiency of light transmitted throughfthe" member 1; I jHowever; theory requiresthat 7 2 fi'with 90f incidence on' the member- 1 theun i 7 i thelring: 11 mustbe shielded:frOrnithelight der's ide: of the membermiist bed'ark; hence which;,would iotherwise; reach lit' u'nder Fthese conditions; For this reasOIIItheshield' 13 is f tiono-f thefldiifusingringll; otherwise the,

r shielding-Twill not :be complete 'Since with Y increasing. angles of'incidence thev shadow V "cast-by; the 7 shield; 13-gradna1ly. covers the diffusing ring." 11,' 'the characteristics-- of;the 5 memberlliand of the diffusing ring' lly mu'st i beisochosenthatwithout the shield lg 'therex willbe?o'verg'compensation, which over- 601161 j' pjensationiis jn'st'correctedby the, action of? the shield 13.1 'Theidiameter and height of thevshield 1'3.may be; chosen so as to 'accom plish this 'purpose;- iLhave 'found" in :prac- I t so added; The height. of; this} shield nnis't be at least as great asithat of "the efiectiveflportic'e that-with a shield'13 of a diameter and heightsubstantially"as shown in Fig; tsuch that the l ray of light following the dotted within certain limitisttoi the right amount. by

" Thei-o'orrect sleeve willlet. in just enough .11 light to supply the deficiency at each angle.

The amount of vcompensatio-n 'atfhigh angles zcani rbe varled varyingthe diameter of I i photometric apparatus beingplaced illuminated side ofthe-testf-plate.

arate pieces as they'ma'y be made a' single f-pieeias shoWn infEig; 7.1 e w: '1

The amount ofnomp'ensation obtained de-f f i pends upon. the relative transparency of the 'membenl-andgring ;11 and upon theirdif filsion-t. If Ythejring 11 is frelatively too opaqueithe memberil will be under-com- "pens'ated; ,;If "the. ring is too transparent thememberl willibe-over-compensated. In, o either casethe compensation. Canbe adjusted substituting sleeves. 1210f difi rent widths.

sirable as practicalmatters'in view of the;

"difliculty'in a'ltering the' inember 1 or: difc fusingring 11; 7 Instead of using theqsleeve v 12 theinneror outer surfaces of the ring yo '11 maybe partly covered with black paint orfinany other way' or two sleeves,,may1be used asshown in Fig 6; The use of'difier ent'materials in'the ring 11 enables the compen'sation"efiectto be-so varied as to' 'bepractically perfect at all angles. .For eXam-,

ple,using-Ta ring' o'f ground glass the com I pensation' can be'made. relatively large at highfangles of incidenceon the member 1; whereas a more perfect diffusing material, 'suchfl as milk glass orfiopal glass depolished gives a more uniform compensating eflect.

- Theinvention may be employed in many ays] Forexampleinstead of -employing l c atransmitting test-plate viewed from the under surface, the'test-plate may be viewed on; its "upper surface by reflected light,- the I i V In the transmittingtype of; "test plate the observer lookstoward the'side ofthe plate on the 'whichisturned away fromthe'illumination to-be-measured", thatis, the-reverserside of the plate. The compensating light 'falls on iv the reverse side of the plate, and thesnm. of the compensating 'g light plus ,the transmitted light'must at all anglesfgive the viewed side of the plate 'anbrightnesslwhich is proportional to theincident illumination on the r obverse-side of the plate. 1;, 7 *Injtherefiectingtype'the side of the plate turned towardthe illumination is: the ob served side.- The difl'usedly reflected light 7 due to the direct illu-minationplus the com-- pensating light which come i through the test platefrom the reverse side must make" the obverse or viewed side of'the platebright,

in proportion tothe incident illumination. As shown in FigxSa plane member 1 of 1 depolishedwhite glass ismounted on slender legs 1' at-a suitable distance above acompensat1ng= plate-1--the #upper vsurface of 'whic'hvis white anddiffusing. The plate lis parallel to and ofthesame size asthe; i,

member 1*andis supported upon an opaque plate liwhich may or may not beprovided with a shield 13.;. In the embodiment of the invention illustrated in Fig. 8jth'e action .is as follows The device is. placed in positioninfrelation to thephotomet'er so that the member 1 can be viewed fromfabover When a V ."the brightness ofth'emember 1 falls oil-r.

due tothe increased angle of incidencei'light.

penetrates the region below the member 1 .1

and striking the compensating plate- 19 is diffusedly reflected'tothe' member 1 cfrom'- the under side thereof and thereby reinforces" v thedirect illumination of the member.-

In accordance withthe provisions of the patent statutes, I have described the princiembodimen t1 "m rely native and that, the in y t w Q1117 inother ways. a a g :l l e qr d my invention, what m; s'lnewandf desire to secure by L t- SBatent,eis: r a Y plane surface located in the place where ber opp site the side on which 1 the n t o to bekmea d testj -pl'ate for} measurement of illung direct light rays; and 'a translucent d ber foradmitting diffusedlight to the test plate; for: measurement of illuation having'pin combination, a member th a translucent" plane surface, and a e her with acylindrical surface to admit "ghttwto; one side of the meinber with the plane surfacefl test-plate for measurement of illufmination, comprising a member with atranslucent plane surface and a diffusing ring-on theside opposite sourceof the illu- 5 e ination, said ring" admitting light to the lluminationw I I @CLA} testplatei for measurement of illuinationi cmprising a member with a lucent j planesurface, a diffusing ring 'ifde of;saidsurface, and an opaque associ'ated 'withsaid lane surface, I a.

' having rajmemberwith a trans with-the said member in combination Tying toprevent over-compensation at angles ofinoidence to themember. A t'est-plateyfor measurement of illuplane surface, a diffusing ring assoted -with the said member in combination screen beyond the perimeter of said g to prevent over-compensation at, high ngles" of incidence to the member, and an pa ue sleeve'associated with said ring. I

A test 'plate for measurement of illunation havingalinember with atranslutgplane surface a diffusing ring assotedw with the said member in combinaionwith' a screen beyond the perimeter of 'd ring toaprevent over-compensation at L I 1,185, 12 a, a h

f mytv invention togetherwiththe aptus which aIlnwgconsiderr to represent aereofgxbut I desire ave it understood yt'hat the? apparatus 1 translucent test plate for -measuref illumination, having means for adlim light; to be measured to both sides A" test-plate for {measurement of v illunation, having a member with a transluuniinatilon is; to: be measured, and n for admitting light to theside of the on,havinga translucent body for reidea of the plane surface, opposite the source ring and adjacent a est-plate a for ig measurement" of illuplane surface, *aj difi'using ring assond a screen beyond the a perimeter" of nationhavinga member with a transluhigh angles of incidence to the member, and an opaque plate between the ring'and the screen, a

10. A test-plate for measurement of illu- Inination comprising amember wit-ha translucent plane'surface, a diffusing rlng, on

fusing ring and extending beyond the perimeterthereof to prevent over-compensation at high angles of incidence to the'member.

11." A translucentfltest-plate for measurement of illumination, having means for ad mitting direct light to one side thereof, and means for admitting difl'usedlight to the other side thereof.

.12. A translucent test-plate for measure- -ment of illumination, having means for admitting direct lightto one side thereof, and

mination, comprising a body of translucent material onone side of which the direct illumination falls, means for indirectly illuminating the reverse side of the body, and,

means whereby the last mentioned illumination is such that the brightness of the observed side of the plate is proportional to the incident flux density on the side directly exposed to the illumination.

16. A test-plate for measurement of illumination, comprising a body [of translucent material on one side of which the direct illumination falls, means for indirectly illuminating the reverse side of the body, and

means whereby the last mentioned illumination is such that the brightness of the observed side of the plate is proportional to the incident flux density of the illumination incident upon the side of the body directly exposed to the illumination irrespective of the angle of incidence of the illumination.

17. In a photometer the combination with a comparison source ofilluminatio-n, of two photometric surfaces, and means for admitting light to be measured to both sides of one of said surfaces. 7 a

18. In a photometer the combination with a comparison source of illumination, of two photometric surfaces, one of said surfaces recelvlng the comparison illumlnation on one side thereof, the other of sa1d surfaces one side of said surface, in combination a with an opaque plate surrounding said dif- I orf' b oth sides thereof.

rec e ivin mbination with (.11 9. Inrzi photoii etei'fthe V00 "Comparisons ou'rce j of illumination, 1 f. two phetomet'ri'csurfaces'fong; of said-"surfaces receivihgj'thfl 'cOmparismi fillumination. on one side thereof; ither :otherbfsziid sflnfaces receiving-116 illumination 'to be measured being-heated befiwenithgplates. V

CLAYTON, HARP; 5 i=1 

